* {
    padding: 0;
    margin: 0;
    letter-spacing: 1px; /* 文字间距 */
}

header, main, header, footer, aside, article, ul, li, div {
    box-sizing: border-box;
}

ul {
    list-style: none;
}

a {
    text-decoration: none;
}

h3 {
    letter-spacing: 3px;
}